The present invention relates to a screw used for fastening parts and in particular to a screw designed so as to prevent loosening and dislodging when male and female threads are engaged.
According to the conventionally used metric screw standard, as shown in FIG. 9, the male screw 1 thread angle is 60 degrees, comprising 30 degree opposing angles with respect to the axial perpendicular plane V. The female screw 2 as well is formed with the same thread angle.
However, in the case of a conventional screw 1 of this type, when a load is applied to the contacting threads during tightening, since the elastic deformation of angles of the male screw 1 exceeds that of the female screw 2, the surface pressure produced by the load in the the flank planes 6 and 8 is not uniform. While flank planes of the male screw 1 and female screw 2 remain in contact, the elastic deformation and load operating center operate eccentrically at the sides of roots of the male screw 1. Consequently, since the torque radius decreases, a problem was encountered whereby the male screw was loosened or dislodged.